Compounds containing perfluoropolyether moieties generally have very small surface free energy to have water and oil repellency, chemical resistance, lubricity, releasing property, and antifouling property. Making use of these properties, they are widely used as, for example, treatment agents to make paper or fiber water- and oil-repellent, and foul-resistant, lubricants for magnetic storage media, oil repellent agents for precision apparatuses, releasing agents, cosmetics, and protective films.
Particularly, a curable perfluoropolyether is used for various applications due to its characteristics of fluoroalkylether. For example, Japanese Patent Application Laid-Open No. 2001-099737 describes a cured product in the form of gel which is resistant to chemicals and solvents, moisture penetration, and is used for a protective coating of a semiconductor pressure sensor and electric circuit.
Meanwhile, it is well known that an organic compound can be bonded to a surface of glass or cloth via a silane coupling agent. The silane coupling agent has an organic functional group and a reactive silyl group, usually an alkoxy silyl group. The alkoxy silyl groups are autocondensed in the presence of moisture to form a siloxane coating film. At the same time, the alkoxy silyl group chemically bonds to glass or metal surface to form a durable film. The silane coupling agents are thus widely used as coating agents for various substrates.
Japanese Patent Application Laid-Open No. S58-167597 discloses a fluoroaminosilane compound represented by the following formula:

wherein R1 and R2 are alkyl groups having 1 to 4 carbon atoms, Q1 is CH2CH2CH2 or CH2CH2NHCH2CH2CH2, h is an integer of from 1 to 4, and i is 2 or 3.
The perfluoropolyether moiety of the compound, however, is relatively short, i.e., from a dimer to a pentamer of hexafluoropropylene oxide, so that the aforesaid characteristics of the perfluoropolyether are not significant.
Japanese Patent Publication of Examined Application No. 6-5324 discloses an antireflection film having improved antifouling property. The layer is formed on an antireflective monolayer or multilayer mainly composed of silicon dioxide deposited by PVD method. The layer is composed of organopolysiloxane polymer or perfluoroalkyl group-containing polymer.
Fouling by human secretion and fingerprint, however, is difficult to wipe off from the layer and tends to extend to form a thin oily film. When it is rubbed strongly, the antireflection film itself is damaged.
Japanese Patent Application Laid-Open No. 11-29585 and 2000-143991 disclose an antireflection film having an antifouling layer prepared from a perfluoropolyether-modified aminosilane represented by the following formula:

wherein X3 is a hydrolyzable group, R5 is a lower alkyl group, R6 is a hydrogen atom or a lower alkyl group, Q2 is CH2CH2CH2 or CH2CH2NHCH2CH2CH2, e is an integer of from 6 to 50, f is 2 or 3, and c and d are integers of from 1 to 3.
Drawbacks of the antireflection film are a relatively long time required to be cured and weak adhesion to a substrate.
Japanese Patent Application Laid-Open No. 2003-238577 discloses a silane coupling agent which contains a perfluoropolyether moiety represented by the following formula:

wherein Rf is a divalent linear perfluoropolyether group, R is a C1-4 alkyl or phenyl group, X is a hydrolyzable group, p is an integer of from 0 to 2, q is an integer of from 1 to 5, and a is 2 or 3.
A coating prepared from the aforesaid silane coupling agent has strong adhesion to a substrate, resistant to fouling and a slick surface resistant to scrubbing.
Even treating a surface with these agents, fouling cannot be prevented perfectly. One has to scrub the surface to remove the fouling quite often. Moreover, the treated surface is not satisfactory in resistance to scrubbing, ease of scrubbing or slickness of the surface.